The effects of Zn vacancies on ferromagnetism in Cu-doped ZnO films controlled by oxygen pressure and Li doping

Zn0.99Cu0.01O films were studied experimentally and theoretically. The films were prepared by pulsed-laser deposition on Pt(111)/Ti/SiO2/Si substrates under various oxygen pressures to investigate the growth-dependence of the ferromagnetic properties. The structural, magnetic, and optical properties were studied, and it was found that all the samples possess a typical wurtzite structure, and that the films exhibit room-temperature ferromagnetism. The sample deposited at 600 ?C and an oxygen pressure of 10 Pa showed a large saturation magnetization of 0.83 ?B/Cu. The enhanced ferromagnetism in the (Cu, Li)-codoped ZnO is attributable to the existence of Zn vacancies (VZn), as shown by first-principles calculations. The photoluminescence analysis demonstrated the existence of VZn in both Zn0.99Cu0.01O and (Cu, Li)-codoped ZnO thin films, and this plays an important role in the increase of ferromagnetism, according to the results of first-principles calculations.